Current responsive electrical circuit breakers typically interrupt electrical circuits in response to the occurrence of selected overload current conditions in the circuits to protect other equipment and wiring in the circuits from damage due to overheating or overcurrent or the like. In one particularly advantageous circuit breaker shown in U.S. Pat. No. 3,361,882 commonly assigned to the assignee of the present invention, the disclosure of which is included herein by this reference, an actuator mechanism manually moves movable contacts into and out of engagement with complementary stationary contacts to make and break a circuit. A current carrying thermostatic trip member is operable to break the circuit in response to the occurrence of a selected overload current in the circuit. The thermostatic trip member is a composite member having a metal layer formed of relatively higher coefficient of expansion and a co-extensive metal layer formed of relatively lower coefficient of expansion arranged so that the layer having the lower coefficient of expansion faces a motion transfer member which is slidably positioned between a portion of the thermostatic trip member which moves with changes in temperature of the thermostatic trip member and a catch assembly. The catch assembly includes a catch surface which interacts with a latch attached to the actuator mechanism. Upon overcurrent conditions the current carrying thermostatic trip member bends thereby moving the motion transfer member which in turn moves the catch assembly releasing the latch to allow the actuator mechanism to move the movable contact and break the circuit. The catch assembly includes a compensator formed of thermostatic material having a layer of relatively higher coefficient of expansion and a layer of relatively lower coefficient of expansion. The compensator is generally U-shaped, having first and second legs extending from a bight with the ends of the legs fixedly attached to a cross-bar of a T-shaped member which extends upwardly between the legs and with the top surface thereof serving as the catch for the latch of the actuator mechanism. The cross-bar is mounted for pivotal motion and is biased toward a normal operating position. The compensator is arranged so that the side having the higher coefficient of expansion faces the trip member. The bight of the U-shaped compensator which is aligned with the motion transfer member moves in the same direction that the trip member moves with changes in temperature to reduce the effect of ambient temperature changes, or in other words, to make the circuit breaker less sensitive to changes in ambient temperature. Thus, the distance between the trip member and the compensator at the location of the motion transfer member stays relatively constant with changes in ambient temperature however, as mentioned above, upon sufficient heating of the trip member due to overcurrent conditions, the trip member will bend toward the compensator causing the motion transfer member to move and the compensator to pivot along with the catch and thereby release the latch to break the circuit.
There are applications, however, in which there is a need to increase sensitivity to ambient temperature changes, at least over a selected range of ambient temperature.